Memory system and information processing system

ABSTRACT

According to one embodiment, a memory system includes a nonvolatile memory, and a controller configured to control the nonvolatile memory. The controller includes an access controller configured to control access to the nonvolatile memory, based on a first request which is issued from an outside, and a processor configured to execute a background process for the nonvolatile memory, based on a second request which is issued from the outside before the first request is issued.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-259951, filed Dec. 24, 2014, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory system and aninformation processing system.

BACKGROUND

There is known a memory system including a nonvolatile semiconductormemory and a control function for controlling the semiconductor memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of aninformation processing system according to a first embodiment.

FIG. 2 is a view illustrating an example of a command frame of a writeprenotification command according to the first embodiment.

FIG. 3 is a flowchart illustrating the issuance of the writeprenotification command according to the first embodiment.

FIG. 4 is a flowchart illustrating the issuance of a write commandaccording to the first embodiment.

FIG. 5 is a flowchart illustrating the generation of a free blockaccording to the first embodiment.

FIG. 5A is a block diagram illustrating an algorithm to obtain a timenecessary for compaction.

FIG. 6 is a flowchart illustrating a write process according to thefirst embodiment.

FIG. 7 is a flowchart illustrating a write termination process accordingto the first embodiment.

FIG. 8 is a timing chart illustrating a background process and a writeprocess according to comparative example 1.

FIG. 9 is a timing chart illustrating a background process and a writeprocess according to the first embodiment.

FIG. 10 is a view illustrating a ratio between write by a host andcompaction write, part (a) being a view illustrating a write ratioaccording to comparative example 1, and a part (b) being a viewillustrating a write ratio according to the first embodiment.

FIG. 11A is a view illustrating a relationship between a block in aninitial state and a valid cluster ratio.

FIG. 11B is a view illustrating a relationship between a block in afirst state and a valid cluster ratio.

FIG. 11C is a view illustrating a relationship between a block in asecond state and a valid cluster ratio.

FIG. 12 is a comparison table illustrating performance of memory systemsaccording to comparative examples 1 and 2 and the first embodiment.

FIG. 13 is a block diagram illustrating a configuration example of aninformation processing system according to a second embodiment.

FIG. 14A is a view illustrating an example of a command frame of acontrol command of preceding execution On/Off according to the secondembodiment.

FIG. 14B is a view illustrating an example of a command frame of arequest for inquiry of a free-area size.

FIG. 14C is a view illustrating an example of a command frame of aresponse to an inquiry of a free-area size.

FIG. 15A is a flowchart illustrating an instruction of precedingexecution On of a background process according to the second embodiment.

FIG. 15B is a flowchart illustrating free block generation according tothe second embodiment.

FIG. 16A is a flowchart illustrating an instruction of precedingexecution Off of the background process according to the secondembodiment.

FIG. 16B is a flowchart illustrating a response to inquiry of generationstatus of free blocks according to the second embodiment.

FIG. 16C is a flowchart illustrating turning preceding backgroundprocess Off according to the second embodiment.

FIG. 17 is a flowchart illustrating issuing write command according tothe second embodiment.

FIG. 18 is a timing chart illustrating a relationship between time and awrite size according to the second embodiment.

FIG. 19 is a block diagram illustrating a configuration example of aninformation processing system according to Modification 1.

FIG. 20 is a flowchart illustrating the issuance of an inquiry and awrite command according to Modification 1.

FIG. 21 is a timing chart illustrating a relationship between time and awrite size according to Modification 1.

FIG. 22 is a block diagram illustrating details of an informationprocessing system according to a third embodiment.

FIG. 23 is a perspective view illustrating a storage system accordingthe third embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a memory system includes anonvolatile memory, and a controller configured to control thenonvolatile memory. The controller includes an access controllerconfigured to control access to the nonvolatile memory, based on a firstrequest which is issued from an outside; a processor configured toexecute garbage collection for securing, on the nonvolatile memory, afree area for writing data in the nonvolatile memory, based on a secondrequest which is issued from the outside before the first request isissued; and a scheduler configured to schedule the garbage collection bycontrolling the processor.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

In the description below, substantially the same functions and elementsare denoted by like reference numerals, and a description will be givenonly where necessary. In addition, in the present specification, aplurality of examples of expression are given to some elements. Theseexamples of expression are merely illustrative examples, and it is notdenied that these elements are expressed by other expressions. Besides,an element, to which a plurality of expressions are not given, may beexpressed by other expressions.

First Embodiment 1. Configuration

[1-1. Configuration of Information Processing System]

To begin with, referring to FIG. 1, a configuration of an informationprocessing system 1 according to a first embodiment is described. FIG. 1is a block diagram illustrating a configuration example of theinformation processing system 1 according to the first embodiment. Asillustrated in FIG. 1, the information processing system 1 includes amemory system 10 and a host 20.

[Memory System 10]

Here, a solid-state drive (SSD) is taken as an example of the memorysystem 10. The memory system 10 includes a NAND flash memory(hereinafter referred to as a “NAND memory”) 11, and a controller 12.

The NAND memory 11 is a nonvolatile memory which is physically composedof a plurality of chips (for example, four chips), although illustrationis omitted here. Each NAND memory 11 is composed of a plurality ofphysical blocks (block 0 to block n) each including a plurality ofmemory cells which are arranged at intersections between word lines andbit lines. In the NAND memory 11, data is erased batch-wise in units ofthis physical block. In short, the physical block is an erase unit.Writing and reading are executed in units of a page (word line) in eachblock.

The controller (memory controller, SSD controller) 12 controls theentire operations of the SSD 10. For example, in accordance with arequest (instruction, command COM, extension command eCOM, etc.) fromthe host 20, the controller 12 controls access to the NAND memory 11(write, read, erase) and a background process BG which is involved in apreceding process. The controller 12 includes a process scheduler 121, abackground processor 122, a requested write size 123, a size of a freearea 124, and a data access controller 125.

The process scheduler 121 transmits a control signal IS to thebackground processor 122 so as to execute a predetermined backgroundprocess, based on an extended command eCOM (second request) which isissued from the host 20, and schedules the background process. Inaddition, based on the received extended command eCOM, the processscheduler 121 returns an extended status signal ReS, which indicates thestate of the self (SSD) 10, to the host 20.

The background processor 122 executes the preceding background processBG for the NAND memory 11.

Here, the background process BG refers to a process which aims atmaintaining the performance of the SSD 10, and is other than a process(write, etc.) responding to a request (first request) from the host 20.Examples of the background process BG include garbage collection, blockerase, and patrol read. As the background process BG, garbage collectionis described here by way of example. The garbage collection(hereinafter, also referred to as “compaction” in some cases) means togenerate free blocks by freeing the area occupied with invalid dataamong the memory areas in the NAND memory 11, and to increase a size ofa free area in the NAND memory 11. The “patrol read” means toperiodically read out data from the NAND memory 11, in order to detectan accumulation of errors mainly due to data retention, before an errorcorrection becomes impossible. It should be noted that the backgroundprocess BG is not limited to these processes, and may include a refreshprocess, for instance. The “refresh process” means that data is readfrom a block in which errors have accumulated, subjected to the errorcorrection, and then written as corrected data to the block.

The requested write size 123 is a size of write requested from the host20.

The size of the free area 124 is a size of the free blocks generated inthe NAND memory 11, which is calculated by multiplying the number offree blocks by the block size, the free blocks being generated bygarbage collection which is the background process BG to be describedlater.

The data access controller 125 controls data access (write, etc.) to theNAND memory 11, in accordance with a request (first request: writecommand COM, etc.) from the host 20, after the above-describedbackground process BG was executed in precedence.

[Host 20]

The host (host apparatus, information process apparatus) 20 drives theSSD 10 and requests write, read and erase of user data from the memorysystem 10. In this case, the host 20 includes, as software components,an operating system 21, a device driver 22, and an application 24. The“erase” refers to an UNMAP(TRIM) and a FORMAT command to erase data inSSD 10, that erases the data which is no longer necessary for the host20.

The operating system (OS, controller) 21 controls the device driver 22and application 24, and controls the entire operations of the host 20.

The device driver 22 controls an SSD controller 23, based on the controlof the operating system 21 or application 24. The SSD controller 23executes predetermined access to the controller 12 in accordance withthe control of the device driver 22.

The application 24 is software which is executed in accordance with thepurpose of a specific work, based on the control of the operating system21.

In the above configuration, the SSD controller 23 of the host 20consciously (intentionally) issues to the SSD 10 an extended commandeCOM (second request) which is a different definition from the write andread command COM (first request). Here, the second request is notlimited to a command form (eCOM), and it should suffice if the secondrequest is some other predetermined extended signal (information,instruction, etc.).

In addition, the controller 12 returns an extended status signal ReS tothe host 20 as a response to the above-described received extendedcommand eCOM. In this case, too, the extended status signal is notlimited to a status signal form (ReS), and it should suffice if theextended status signal is some other predetermined extended signal(information, return signal, response, etc.).

Accordingly, the host 20 can detect at least the state of the NANDmemory 11, based on the returned extended status signal ReS. As aresult, the host 20 can instruct a background process (for example,garbage collection, etc.) in accordance with the detected state of theNAND memory 11, etc. The details will be described later.

It should be noted that the order of transmission of the above-describedextended command eCOM and extended status signal ReS is not particularlylimited. Specifically, an extended predetermined signal may first betransmitted from the SSD 10 to the host 20, and then an extendedpredetermined signal may be transmitted from the host apparatus 20 tothe SSD 10.

[1-2. Command Frame (Write Prenotification Command)]

Next, referring to FIG. 2, a description is given of a command frame ofthe extended command eCOM according to the first embodiment. Here, awrite prenotification command eCOM is taken as an example of theextended command.

As illustrated in FIG. 2, the write prenotification command eCOM iscomposed of a write size and a write schedule time as its command frame.For example, in the write prenotification command eCOM according to thefirst embodiment, the write size is 10 GB, and the write schedule timeis 60 seconds later from the present time that is issued time of thecommand eCOM.

It should be noted that the command frame of the write prenotificationcommand eCOM is not limited to that illustrated in FIG. 2. For example,the write prenotification command eCOM may include, as well as the writeprenotification time, hint information which can specify a write starttime.

2. Background Process and Write Operation

Next, in the above-described configuration, a background process and awrite operation are described.

[2-1. Operation on Host 20 Side]

To begin with, referring to FIG. 3 and FIG. 4, the operation on the host20 side is described.

As illustrated in FIG. 3, in step S11, the SSD controller 23 on the host20 side recognizes a write prenotification, based on an instruction fromthe device driver 22.

In step S12, the SSD controller 23 issues a write prenotificationcommand eCOM, which is an extended command, to the SSD 10.

In the meantime, based on the received write prenotification commandeCOM, the controller 12 returns to the host apparatus 20 an extendedstatus signal ReS which indicates the state of the free blocks in theNAND memory 11. The details will be described with reference to FIG. 5.

Subsequently, based on the returned status signal ReS, the host 20detects the size of the free area 124 in the NAND memory 11.Accordingly, as illustrated in FIG. 4, in step S21, the SSD controller23 issues a write command COM to the SSD 10, based on the status signalReS.

[2-2. Operation on SSD 10 Side]

Next, referring to FIG. 5 to FIG. 7, the operation on the SSD 10 side isdescribed.

[2-2-1. Free Block Generation (Preceding Background Process)]

To start with, the controller 12 on the SSD 10 side executes anoperation illustrated in FIG. 5.

In step S13 of FIG. 5, upon receiving the write prenotification commandeCOM, the process scheduler 121 of the controller 12 transmits a controlsignal IS to the background processor 122, so as to execute garbagecollection. The background processor 122, which received the controlsignal IS, determines whether the requested write size (the write size:10 GB) 123 described in the received prenotification command eCOM ismore than the limit value of the size of the free area 124 in the NANDmemory 11. The “limit value” is a predetermined value used to limit thetotal size of the free area 124 including the free area generated by theinstruction from the host 20 in this embodiment. To be more specific,the process scheduler 121 compares the write size 10 GB of the writeprenotification command eCOM and the limit value of the size of the freearea 124 in the NAND memory 11. Then, the background processor 122determines whether the write size 10 GB is more than the limit value ofthe size of the free area 124 in the NAND memory 11, and returns adetermination result to the process scheduler 121.

In step S14, based on the above determination result, if the requestedwrite size 123 exceeds the limit value of the size of the free area 124in the NAND memory 11 (No in S13), the process scheduler 121 controlsthe background processor 122 so as to change the requested write size123 to the limit value of the size of the free area 124.

In step S15, based on the above determination result, if the requestedwrite size 123 is less than or equal to the limit value of the size ofthe free area 124 in the NAND memory 11 (Yes in S13), the processscheduler 121 calculates a generation size in the free area 124 in theNAND memory 11. Specifically, the controller 12 calculates thegeneration size by subtracting the present size of the free area 124from the requested write size 123. Here, the “free area” in the NANDmemory 11 refers to an area, in which write can be executed to the NANDmemory 11, without garbage collection (compaction) being carried out.

In step S16, the process scheduler 121 determines whether a time, whichis calculated by subtracting the time necessary for compaction (CMP)from the write time specified in the write prenotification command eCOM,is a present time or later (the time interval is positive or not).Specifically, the process scheduler 121 determines whether a time, whichis calculated by subtracting the time necessary for CMP from the writeschedule time “60 seconds later” of the write prenotification commandeCOM, is a present time or later.

Here, the time necessary for compaction (CMP) can be calculated byadding the time required for compaction of a number of source blocks togenerate a number of free blocks corresponding to the generation size.The compaction time of each block can be calculated from the validcluster ratio (valid cluster counter) of the block. The “valid/invalidclusters” are clusters written in blocks in the NAND memory 11, andthose which referred to by LUT are valid clusters, whereas those notreferred to by LUT are invalid clusters. It should be noted that theblock (compaction source block), which is a target of compaction, isselected from the blocks with the least valid cluster ratios.

An algorithm to obtain the time necessary for compaction will beexplained with reference to FIG. 5A.

Here, it can be approximated that a plurality of source blocks are equalto each other in valid cluster ratio (valid cluster ratio) R, in thefollowing conditions. More specifically, first, the number of sourceblocks required is sufficiently less as compared to the number of blockscorresponding to the physical capacity or the overprovisioning capacity.Further, there is a correlation between (the size of) the number ofsource blocks and the size of the write request from the host.

FIG. 5A illustrates the case where valid data contained in three sourceblocks each having a valid cluster ratio R of 1/3 is written in onedestination block. Thus, three free blocks are generated, and one freeblock is consumed. As a result, two free blocks can be obtained. Inother words, when the valid cluster ratio R of a source block is 1/3,two free blocks can be obtained while writing in one destination block.

The example of FIG. 5A will be generalized. One free block is obtainedby executing compaction of the valid data included in 1/(1−R) sourceblocks, having the valid cluster ratio R, to R/(1−R) destination blocks.By repeating the above process for f times, f free blocks are obtained.In other words, the compaction write size is proportional to f*(R/(1−R))while obtaining free blocks. Here, f is the number of free blocksrequired to be additionally generated, which is calculated by dividingthe generation size by the block size. R is the valid cluster ratio ofthe source block at the present time.

Here, the time required for one block compaction write is defined as acoefficient α. The time necessary for compaction to obtain f free blocksis proportional to the compaction write size. As a result, the timenecessary for compaction can be obtained using the coefficient α in thefollowing equation (I).

f*(R/(1−R))*α  (I)

In step S17, in the case of “True” in step S16, the process scheduler121 sets this time in a timer (not shown) for the next start.

In step S18, in the case of “False” in step S16, the process scheduler121 determines whether the requested write size 123 is less than orequal to the size of the free area 124 in the NAND memory 11 which wasset in step S15. The reason for this is that, with an elapsed time fromstep S15 to S18, the size of the free area 124 in the NAND memory 11 mayfail to satisfy the requested write size of the host 20. To be morespecific, there is a case where the memory system 10 receives an extrawrite request, from the host or another host, other than the writerequest prenotified with the eCOM. In this case, a part of the generatedfree area 124 may be consumed with the extra write request, resulting ina decrease of the size of the free area 124. For example, there may be acase that plural hosts 20 exist.

Specifically, in step S18, the background processor 122, which receivedan instruction of the process scheduler 121, determines whether therequested write size 123 is less than or equal to the size of the freearea 124.

In step S19, if the requested write size 123 is less than the size ofthe free area 124 (No in S18), the process scheduler 121 controls NANDmemory 11 to perform compaction for one block of the NAND memory 11.Specifically, if the condition in step S18 is not satisfied (No in S18),the background processor 122, which received the control signal IS fromthe process scheduler 121, further executes, prior to write, garbagecollection (compaction) as the background process BG for one block ofthe NAND memory 11. Subsequently, the scheduler 121 repeats this stepS19 until satisfying the condition of step S18.

At last, if the requested write size 123 is less than or equal to thesize of the free area 124 in the NAND memory 11, which was set in stepS15 (Yes in S18), the process scheduler 121 returns to the host 20 anextended status signal ReS.

[2-2-2. Write Operation]

Here, the host 20 issues the write command COM illustrated in FIG. 4 tothe controller 12 of the SSD 10, based on the extended status signal ReSwhich was returned from the SSD 10.

Next, the controller 12, which received the write command COM, executesa write operation illustrated in FIG. 6.

In step S22, the data access controller 125 of the controller 12determines whether there is a background process BG which is executedprecedent to this write.

In step S23, if there is a background process BG which is executedprecedent to the write (Yes in S22), the data access controller 125temporarily stops the preceding background process BG.

In step S24, if there is no background process BG which has higherpriority than the write (No in S22), the data access controller 125determines whether there is a background process BG with a prioritywhich can be lowered.

In step S25, if there is a background process BG with a priority whichcan be lowered (Yes in S24), the data access controller 125 lowers thepriority of the other background process (for example, other garbagecollection, block erase, etc.).

In step S26, if there is no background process BG with a priority whichcan be lowered (No in S24), the data access controller 125 writes writedata into the NAND memory 11 at address, based on the write command COM.

[2-2-3. Write Termination Process]

Here, based on the write command COM, the data access controller 125writes write data into the NAND memory 11 at addresses, and thenexecutes a write termination process illustrated in FIG. 7.

In step S31, the data access controller 125 determines whether there isa background process which is temporarily stopped in the precedingexecution background processes BG.

In step S33, if there is a temporarily stopped background process in thepreceding execution background processes BG (Yes in S31), the dataaccess controller 125 resumes the preceding execution of this backgroundprocess.

In step S32, if there is no temporarily stopped background process inthe preceding execution background processes BG (No in S31), the dataaccess controller 125 determines whether there is a background processBG with a lowered priority. If there is no background process BG with alowered priority (No in S32), the data access controller 125 terminatesthis operation.

In step S34, if there is a background process BG with a lowered priority(Yes in S32), the data access controller 125 raises the priority of thisbackground process BG and terminates this operation.

3. Advantageous Effects

As has been described above, according to the configuration andoperation of the information processing system 1 of the firstembodiment, at least the following advantageous effects of (1) to (5)can be obtained. The description below is given by comparing, wherenecessary, the cases of comparative examples 1 and 2 and the case of thefirst embodiment.

(1) The Write Performance can be Enhanced, and Latency can be Reduced.

A) Case of Comparative Example 1

Here, comparative example 1 is a memory system in which, unlike thefirst embodiment, the background process (garbage collection) is notexecuted in precedence.

Thus, as illustrated in FIG. 8, in the memory system according tocomparative example 1, a background process (garbage collection) BGA andBGB for securing a free block needs to be executed concurrently with thewrite process WA and WB. For example, as illustrated in FIG. 8, in thecomparative example 1, at time t1, the background process BGA and writeprocess WA are started. Subsequently, at time t2, after the end of thewrite process WA, the background process BGB and write process WB arestarted. Thus, at time t3, all write operations are completed.

In this manner, in comparative example 1, in the write process WA andWB, the background process BGA and BGB needs to be also executedconcurrently. Thus, in comparative example 1, all of the performance ofwrite to the NAND memory cannot be allocated to the write process. As aresult, comparative example 1 is disadvantageous in that the writeperformance decreases and the latency increases.

B) Case of the First Embodiment

Compared to the above-described comparative example 1, in the firstembodiment, the scheduler 121 controls the background processor 122 bythe control signal IS so as to execute a predetermined backgroundprocess, based on the extended command eCOM (second request) which isissued from the host 20. Hence, based on the control signal IS, thebackground processor 122 executes the background process BG for the NANDmemory 11 preceding the access (write, etc.) (FIG. 5, etc.).

For example, as illustrated in FIG. 9, in the first embodiment, at timet0, the background processor 122 starts the background process (garbagecollection) BGA and BGB, prior to write.

Thus, at time t1, in the state in which the background processes BGA andBGB have all been completed, the write process WA and WB can be started.

As a result, at time t2, the write process WA and WB can be completed.

In this manner, in the first embodiment, since all the performance ofwrite to the NAND memory 11 can be allocated to the write process WA andWB, the write performance can be enhanced. Furthermore, in a typicalcase, the latency can advantageously be reduced by time TO, compared tocomparative example 1.

(2) The Ratio of Write can be Improved.

As illustrated in part (a) of FIG. 10, the ratio between write andcompaction (garbage collection) according to comparative example 1 is,for example, about 1:1.

By contrast, in the information processing system 1 according to thefirst embodiment, by the execution of preceding garbage collection (forexample, S19 in FIG. 5) by the host instruction eCOM, it is possible togenerate an allowance in the size of a free area for a subsequent write.By the allowance in size of the free block, the ratio of compactionwrite can greatly be decreased, compared to the ratio of write, and,ideally, the ratio of compaction write can be reduced to substantiallyzero. Thus, as illustrated in part (b) of FIG. 10, in the firstembodiment, the ratio between write and compaction (garbage collection)can be set at about 1:0. In this manner, in the first embodiment, theratio of write can be improved.

(3) Write-Amplification Factor (WAF) can be Decreased.

This advantage will be described by comparing comparative example 2 andthe first embodiment with reference to FIG. 11A to FIG. 11C. FIG. 11A toFIG. 11C are views illustrating the relationship between blocks BK andvalid cluster ratios, FIG. 11A to FIG. 11C showing valid clusterdistributions over physical blocks in an initial state, a first stateand a second state, respectively. It should be noted that, in FIG. 11Ato FIG. 11C, the size of the hatched areas which correspond to the usercapacity of the SSD 10 are equal to each other.

Here, garbage collection is executed for a target of a block (compactionsource block) CBK having a least valid cluster ratio. For example, inthe initial state of FIG. 11A, since the valid cluster ratio issubstantially equally 100%, compaction is executed for the 5th block asa target. On the other hand, in the first and second states of FIG. 11Band FIG. 11C, compaction is executed for the 7th block and the 10thblock as targets.

A) Case of Comparative Example 2

Here, comparative example 2 is a memory system which is a drive side andgreedily executes preceding compaction. Thus, as indicated in thefollowing two points (a1 and a2), the memory system according tocomparative example 2 needs to execute a large amount of garbagecollection (compaction).

Point a1) Compaction has to be executed for a compaction source blockwith a higher valid cluster ratio.

In the case of comparative example 2, in an extreme case, if there is anallowance in time, the memory system maximizes the number of freeblocks, and tries to maintain the peak performance as much as possibleat the next write request. This corresponds to the case in which thememory system tries to maintain the initial state of FIG. 11A if thereis an allowance in time. Specifically, in comparative example 2, in theinitial state of FIG. 11A, the amount of compaction, which is necessaryfor creating one free block, is large.

Point a2) A large amount of compaction has to be executed until reachingthe initial state of FIG. 11A from the second state of FIG. 11C.

Here, after a write request from the host continued, a transition hasoccurred to the second state of FIG. 11C. Thus, in comparative example2, whenever the time allows, compaction is frequently executed so that atransition may occur from the second state of FIG. 11C to the initialstate of FIG. 11A. To put it simply, in order to generate many freeblocks, it is necessary to execute a large amount of compaction.

In this manner, in comparative example 2, as a result of the above twopoints, since a large amount of compaction needs to be executed as awhole, WAF is larger.

It should be noted that, in the case of comparative example 1, a garbagecollection process is not preceding execution. Thus, in the second stateof FIG. 11C, compaction is constantly executed. Accordingly, the validcluster ratio of the compaction source drops to as low as about 20%, andhence WAF is low. However, in the case of comparative example 1, sincethe number of free blocks is always small, comparative example 1 isdisadvantageous in that the ratio of write is low, and the peakperformance is low.

B) Case of the First Embodiment

By contrast, in the first embodiment, based on the instruction (eCOM) ofthe host 20 which is the device driver side, the garbage collectionprocess is precedently executed. According to this, the memory system 10generates the size of the free area 124 when needed in accordance withthe required write size.

As a result, an inefficient, useless compaction, as in comparativeexample 2, can be avoided. In addition, unlike comparative example 1,the ratio of write does not decrease, and the peak performance can beimproved.

(4) The Peak Power Consumption can be Reduced.

As described above, in the first embodiment, prior to write, the garbagecollection process BG is precedently executed. In other words, the writeand garbage collection process BG can be executed in a temporallydistributed manner. Thus, the first embodiment is advantageous in that,since these two operations are processed in a temporally distributedmanner, the power consumption involved in the process can bedistributed, and the peak power consumption can be reduced.

(5) As regards the other background process such as block erase, thesame advantageous effects as in the above (1) to (4) can be obtained.

As illustrated in FIG. 12, if the advantageous effects of theabove-described comparative examples 1 and 2 and first embodiment aresummarized, the method of maximization of peak performance is, incomparative example 2, greedy garbage collection at the discretion ofthe SSD (drive) itself. On the other hand, the first embodiment isdifferent with respect to the preceding garbage collection on theinstruction (eCOM) of the host 20.

Thus, the peak performance is high in each of the comparative example 2and the first embodiment. However, while the preceding compaction amountis excessively large in comparative example 2, the amount that is atotal amount of the generated free blocks necessary for the peakperformance based on the host instruction (eCOM) can be obtained in thefirst embodiment. In addition, as described in the above (3), the WAF incomparative example 2 is larger than that in the first embodiment.

The advantageous effects as described above are not limited to thegarbage collection (compaction). Specifically, needless to say, the sameadvantageous effects as in the above (1) to (4) can be obtained withrespect to the other background processes such as block erase and patrolread.

Second Embodiment The Host Explicitly Requests Switching on/Off of thePreceding Background Process

Next, referring to FIG. 13 to FIG. 18, an information processing systemaccording to a second embodiment is described. The second embodimentrelates to an example in which the host 20 requests, from the SSD 10,switching On/Off of the preceding background process. In the descriptionbelow, a detailed description of the configurations and operations,which overlap those of the first embodiment, is omitted.

[Information Processing System]

Referring to FIG. 13, a configuration of an information processingsystem 1 according to the second embodiment is described. As illustratedin FIG. 13, the second embodiment differs from the first embodiment inthat the information processing system 1 according to the secondembodiment does not include the process scheduler 121, and the extendedcommand eCOM1, eCOM2 is transmitted from the host 20 to the backgroundprocessor 122.

The host 20 transmits the extended command eCOM1 to the backgroundprocessor 122, thereby controlling On (execution) or Off (non-execution)of preceding execution of the background process. Further, the host 20transmits the extended command eCOM2 to the background processor 122,thereby requesting inquiry of the free-area size in the NAND memory 11,and checking the status of the free area.

The background processor 122, which received the extended command eCOM1,eCOM2, returns to the host 20 an extended status signal ReS based onthis extended command. For example, the background processor 122, whichreceived the extended command eCOM2, notifies the host 20 of the size ofthe free area in the NAND memory 11 as the content of the extendedstatus signal ReS based on the command eCOM2. The details of these willbe described later.

[Command Frame (eCOM1, eCOM2, ReS)]

Referring to FIG. 14, a description is given of command frames of theextended commands and status signal according to the second embodiment.

As illustrated in FIG. 14A, the extended command eCOM1 according to thesecond embodiment is composed of a control flag of On/Off of precedingexecution, and a requested write size. For example, when the precedingexecution of the background process is requested to be On, the controlflag of the extended command eCOM1 is set. And when the precedingexecution of the background process is requested to be Off, the controlflag of the extended command eCOM1 is set in a “0” state.

As illustrated in FIG. 14B, a parameter is not particularly set for theextended command eCOM2 according, to the second embodiment. The extendedcommand eCOM2 is composed such that the extended command eCOM2 has adifferent definition from other write command COM, etc., to inquire thesize of the free area in the NAND memory 11. The “free area” in the NANDmemory 11 refers to an area, which enables writing to the NAND memory 11without executing garbage collection (compaction).

As illustrated in FIG. 14C, the extended status signal ReS according tothe second embodiment is composed of a size of the free area, which iscalculated from the number of free blocks, as a return signal of theextended command eCOM2. For example, the content of the size of the freearea of the extended status signal ReS according to the secondembodiment is described as 5 GB.

[Background Process and Write Operation]

Next, a background process and a write operation in the above-describedconfiguration are described. In the description below, the backgroundprocess and write operation are described as a series of operations onthe host 20 side and SSD 10 side.

[Operation of Preceding Execution on of the Background Process]

As illustrated in FIG. 15A, in step S41, the SSD controller 23 of thehost 20 recognizes write prenotification based on an instruction of thedevice driver 22.

In step S41, the SSD controller 23 issues an extended command eCOM1 ofpreceding execution On to the background processor 122. To be morespecific, the SSD controller 23 issues an extended command eCOM1 withthe control flag of the “1” state to the background processor 122, so asto execute preceding execution of the background process.

Subsequently, as illustrated in FIG. 15B, the background processor 122,which received the extended command eCOM1, first starts the precedingexecution of the background process, since the control flag of thecommand eCOM1 is in the “1” state.

Next, in step S43, the background processor 122 determines whether therequested write size described in the received command eCOM1 is lessthan or equal to the limit value of the size of the free area 124 in theNAND memory 11. To be more specific, the background processor 122compares the write size 10 GB of the command eCOM1 and the limit valueof the size of the free area 124 in the NAND memory 11. Then, thebackground processor 122 determines whether the write size 10 GB is lessthan or equal to the limit value of the size of the free area 124 in theNAND memory 11.

In step S44, if the requested write size 123 is greater than the limitvalue of the size of the free area 124 in the NAND memory 11 (No inS43), the background processor 122 changes the requested write size tothe limit value of the size of the free area 124.

In step S45, if the requested write size is less than or equal to thelimit value of the size of the free area 124 in the NAND memory 11 (Yesin S43), the background processor 122 determines whether the requestedwrite size of the command eCOM1 is less than or equal to the size of thefree area 124 in the NAND memory 11 which was set in step S43. This isbecause with an elapsed time, the size of the free area in the NANDmemory 11 may fail to satisfy the requested write size of the host 20.To be more specific, there is a case where the memory system 10 receivesan extra write request, from the host or another host, other than thewrite request pre-notified with the eCOM. In this case, a part of thegenerated free blocks may be consumed with the extra write request,resulting in a decrease of the number of free blocks.

In step S46, if the requested write size is larger than the size of thefree area 124 (No in S45), the background processor 122 controls toperform compaction of one block of the NAND memory 11. Specifically, inthis case, the background processor 122 executes, prior to write,garbage collection (compaction) in advance as the background process BGfor one block of the NAND memory 11. Subsequently, the backgroundprocessor 122 repeats this step S46 until satisfying the condition ofstep S45.

At last, if the condition of step S45 is satisfied (Yes in S45), thebackground processor 122 returns to the host 20 an extended statussignal ReS which is indicative of the size of the free area (forexample, 5 GB) which is calculated from the number of free blocks.

[Operation of Preceding Execution Off of the Background Process]

As illustrated in FIG. 16A, in step S51, based on an instruction of thedevice driver 22, the SSD controller 23 of the host 20 issues anextended command eCOM2 to the background processor 122 of the SSD 10, asan inquiry of the generation status of the free blocks in the SSD 10.

In step S52, based on an extended status signal ReS (to be describedlater in detail with reference to FIG. 16B) which was returned from thebackground processor 122, the SSD controller 23 determines whether thesize of the free area in the SSD 10 (size 5 GB of free area of ReS) hasreached an instructed value.

In step S53, if the size of the free area in the SSD 10 has not reachedthe instructed value (No in S52), the SSD controller 23 sets a timer(not shown) for the next time.

In step S54, if the size of the free area in the SSD 10 has reached theinstructed value (Yes in S52), the SSD controller 23 issues a commandeCOM1 by which the preceding execution of the background process in theOff state. Specifically, the SSD controller 23 issues to the backgroundprocessor 122 the extended command eCOM1 with the flag in the “0” state,so as not to carry out the preceding execution of the backgroundprocess.

As illustrated in step S55 of FIG. 16B, the background processor 122,which received the extended command eCOM2 as the inquiry of thegeneration status of the free blocks in step S51 of FIG. 16A, acquiresthe number of free blocks. Specifically, the background processor 122acquires the number of free blocks which can be used up for write to theNAND memory 11.

In step S56, the background processor 122 calculates the size of thefree area. Specifically, the background processor 122 multiplies thenumber of free blocks, which was acquired in step S55, by the blocksize, and calculates the size of the free area.

In step S57, the background processor 122 transmits to the host 20 astatus signal ReS describing the size (for example, 5 GB) of the freearea calculated in step S56.

In step S58 of FIG. 16C, the background processor 122, which receivedthe extended command eCOM1 in step S54 of FIG. 16A, determines whetherthere is a background process BG which is being executed in precedence.If the condition of step S58 is not satisfied (No in S58), thebackground processor 122 terminates the operation of turning precedingbackground process Off.

In step S59, if the condition of step S58 is satisfied (Yes in S58), thebackground processor 122 stops the background process (for example,garbage collection process) BG which is being executed.

[Issuing Write Command]

As illustrated in FIG. 17, at a time of issuing a write command COM, theSSD controller 23 determines, in step S61, whether the precedingexecution of the background process BG is in the On state or not. Ifthis condition of step S61 is not satisfied (No in S61), the processgoes to step S63.

In step S62, in order to set the preceding execution of the backgroundprocess BG into the Off state, the SSD controller 23 issues to the SSD10 an extended command eCOM1 with the control flag indicating the “0”state.

In step S63, the SSD controller 23 receives a status signal ReS from thebackground processor 122, and issues a write command COM to the SSD 10.

The write operation executed by the data access controller 125 afterreceiving the write command COM are substantially the same as those inthe above-described first embodiment. Thus, a detailed descriptionthereof is omitted.

Advantageous Effects

As has been described above, according to the information processingsystem 1 of the second embodiment, at least the same advantageouseffects as the above-described (1) to (5) can be obtained.

Here, in the second embodiment, the host 20 transmits the extendedcommand eCOM1 to the SSD 10, and requests switching On/Off of thepreceding background process (FIG. 14A, FIG. 15A). When switching thepreceding execution On was requested, the background processor 122 ofthe SSD 10, which received this command eCOM1, executes garbagecollection as the background process, prior to the write operation (FIG.15B). Thereby, the background processor 122 continues to generate freeblocks until the size of the free area 124 reaches the requested writesize 123 (FIG. 15B). Thus, before the write, the sufficient number offree blocks can be secured. In addition, in the case of executing write,the host 20 sets the preceding execution of the background process ofthe SSD 10 in the Off state (FIG. 16A to FIG. 16C, FIG. 17).

Furthermore, in the second embodiment, the host 20 issues an inquiry tothe SSD 10 by sending the extended command eCOM2, and monitors thegeneration status of the free blocks in the SSD 10 (S51 to S52 of FIG.16A, etc.).

For example, the above control, which is executed by the informationprocessing system 1 of the second embodiment, is illustrated as shown inFIG. 18.

As illustrated in FIG. 18, at time t1, the host 20 transmits the commandeCOM2 to the SSD 10, and executes check 1 of the generation status ofthe free blocks in the SSD 10.

At time t2, based on the check result of the check 1, the host 20transmits the command eCOM1 to the SSD 10, and requests On of precedingexecution of the garbage collection as the background process.

At time t3 and time t4, the host 20 similarly transmits the commandeCOM2 to the SSD 10, and executes check 2 and check 3 of the generationstatus of the free blocks in the SSD 10.

At time t5 immediately before write, the host 20 transmits the commandeCOM1 to the SSD 10, based on the check result of the check 3, andrequests Off of preceding execution of the garbage collection as thebackground process.

In this manner, according to the second embodiment, the selectivity ofthe information processing system 1 can be broad, without the provisionof the process scheduler 121. In addition, where necessary, the secondembodiment can be applied.

(Modification 1)

Next, referring to FIG. 19 to FIG. 21, an information processing systemaccording to Modification 1 is described. Modification 1 is an exampleof a variation of the second embodiment. In the description below, adetailed description of the configurations and operations, which overlapthose of the first and second embodiments, is omitted.

[Information Processing System]

Referring to FIG. 19, a configuration of an information processingsystem 1 according to Modification 1 is described. As illustrated inFIG. 19, Modification 1 differs from the second embodiment in that theinformation processing system 1 according to Modification 1 does notinclude the requested write size 123.

Since the other configuration is substantially the same as in the secondembodiment, a detailed description thereof is omitted.

[Issuing Inquiry and Write Command]

Referring to FIG. 20, a description is given of issuance operations ofan inquiry and a write command of the information processing system 1according to Modification 1. It is now assumed that the garbagecollection as the background process BG is being executed in precedenceby the extended command eCOM1 which was transmitted from the host 20.

In step S71, the SSD controller 23 of the host 20 issues an extendedcommand eCOM2 to the background processor 122, and inquires about thegeneration status of the free blocks generated by the background processBG executed in precedence. The background processor 122, which receivedthe inquiry, returns the size of the free area 124 to the SSD controller23 by an extended status signal ReS.

In step S72, the SSD controller 23 determines whether the requestedwrite size, which the host 20 requires to execute to the memory system1, is larger than the size of the free area 124. To be more specific,based on the size of the free area 124 which is described in thereturned status signal ReS, the SSD controller 23 determines whether thewrite size required by the host 20 is larger than the size of the freearea 124. If the condition of step S72 is not satisfied (No in S72), theprocess goes to step S74.

In step S73, if the requested write size, which the host 20 requires toexecute to the memory system 1, is larger than the size of the free area124 (Yes in S72), the SSD controller 23 makes the write size regulatedto the size of the free area 124.

In step S74, based on the set size, the SSD controller 23 issues a writecommand COM to the data access controller 125. To be more specific, inthe case of “No” in S72, the size of the free area 124, which wasgenerated by the background process BG that was executed in precedence,is larger than the write size required by the host 20. Thus, the SSDcontroller 23 issues the write command COM so as to execute write, basedon the set size (the write size). On the other hand, in the case ofcontinuance from S73, the SSD controller 23 issues the write command COMso as that the requested write size is equalized to the size of the freearea 124.

Since the preceding execution On/Off of other background processes andwrite operation are substantially the same as in the first and secondembodiments, detailed description thereof is omitted.

Advantageous Effects

As has been described above, according to the information processingsystem 1 of Modification 1, at least the same advantageous effects asthe above-described (1) to (5) can be obtained.

Here, according to Modification 1, the host 20 issues the command eCOM2to the SSD 10 and inquires about the generation status of the freeblocks 124 in the SSD 10 (S71 in FIG. 20). Then the host 20 writes thedata of the size of the free area, based on the inquiry (S72 to S74 inFIG. 20). In other words, in Modification 1, even in the case where theSSD 10 is executing the background process BG in precedence and the sizeof the free area 124 fails to meet the requested write size 123, thehost 20 executes write for an acceptable write size in accordance withthe size of the free area 124 (S73 in FIG. 20). In addition, even in thecase where the host 20 has not issued an instruction of precedingexecution On of the background process BG, the host 20 can write for upto the acceptable write size in accordance with the size of the freearea in the NAND memory 11.

For example, the control, which is executed by the informationprocessing system 1 of Modification 1, is illustrated as shown in FIG.21.

As illustrated in FIG. 21, at time t1, the host 20 issues the commandeCOM2 to the SSD 10, and executes check 1 of the generation status ofthe free blocks 124 in the SSD 10 (S71 in FIG. 20).

At time t2, based on the check result of the check 1, the host 20transmits the command eCOM1 to the SSD 10, and requests On of precedingexecution of the garbage collection as the background process.

At time t3, the host 20 similarly issues the command eCOM2 to the SSD10, and executes check 2 of the generation status of the free blocks 124in the SSD 10.

At time t4, the host 20 issues the write command COM to the SSD 10,based on the size 1 GB described in the extended status signal ReS,which is the check result of the check 2, and causes the SSD 10 toexecute write of the size 1 GB.

In this manner, according to Modification 1, the selectivity of theinformation processing system 1 can be broad, without the provision ofthe process scheduler 121 and the requested write size 123. In addition,where necessary, Modification 1 can be applied.

Third Embodiment

In a third embodiment, a detailed configuration of the informationprocessing system 1, which has been described in the first and secondembodiments and Modification 1, is described.

[Detailed Configuration of Information Processing System 1]

FIG. 22 is a block diagram illustrating an example of the detailedconfiguration of an information processing system 1 according to thethird embodiment. In FIG. 22, the process scheduler 121 and backgroundprocessor 122 according to the above-described first and secondembodiments and Modification 1 correspond to, for example, a CPU 43B,etc. In addition, the data access controller 125 according to theabove-described first and second embodiments and Modification 1corresponds to, for example, a host interface 41, etc. The requestedwrite size 123 and the size of the free area 124 may be located in avolatile memory and used.

As illustrated in FIG. 22, the controller 12 includes a front end 12Fand a back end 12B.

The front end (host communication unit) 12F includes the host interface41, a host interface controller 42, an encryption/decryption unit(Advanced Encryption Standard [AES]) 44, and the CPU 43F.

The host interface 41 communicates with the information processingapparatus 20 for communication of requests (write command, read command,erase command (UNMAP(TRIM) command), etc.), logical addresses LBA, anddata.

The host controller (controller) 42 controls the communication of thehost interface 41, based on the control of the CPU 43F.

The encryption/decryption unit (Advanced Encryption Standard [AES]) 44encrypts, in a write operation, write data (plain text) which is sentfrom the host interface controller 42. The encryption/decryption unit 44decrypts, in a read operation, encrypted read data which is sent from aread buffer RB of the back end 12B. It should be noted that, wherenecessary, write data and read data can be transmitted without theintervention of the encryption/decryption unit 44.

The CPU 43F controls the respective components 41, 42 and 44 of thefront end 12F, and controls the entire operations of the front end 12F.

The back end (memory communication unit) 12B includes a write buffer WB,the read buffer RB, an LUT unit 45, a DDRC 46, a DRAM 47, a DMAC 48, anECC 49, a randomizer RZ, a NANDC 50, and a CPU 43B.

The write buffer (write data transfer unit) WB temporarily stores writedata WD which is transmitted from the host 20. Specifically, the writebuffer WB temporarily stores data until the size of the write data WDreaches a predetermined size that is suited to the NAND memory 11.

The read buffer (read data transfer unit) RB temporarily stores readdata RD which was read out from the NAND memory 11. Specifically, in theread buffer RB, the read data RD is rearranged in an order suited to thehost 20 (an order of logical addresses LBA which is designated by thehost 20).

The look-up table (LUT) 45 is a conversion table to convert the logicaladdress LBA to a corresponding physical address PBA.

The DDRC 46 controls a double data rate (DDR) in the DRAM 47.

The dynamic random access memory (DRAM) 47 is, for example, a volatilememory which stores the LUT 45.

The direct memory access controller (DMAC) 48 transfers write data WDand read data RD via an internal bus IB. In FIG. 22, although one DMAC48 is illustrated, the controller 12 may include two or more DMACs 48.The DMAC 48 is set at various positions in the controller 12, wherenecessary.

The error correction unit (ECU) 49 adds an error correction code (ECC)to the write data WD which is sent from the write buffer WB. The ECC 49corrects, where necessary, the read data RD which was read out from theNAND memory 11, by using the added ECC, when the ECC 49 sends the readdata RD to the read buffer RB.

The randomizer (or scrambler) RZ is configured to equalize the frequencyof being programmed as 1 and that as 0 for each cell (wear leveling foreach cell) and to suppress unevenness in the numbers of 1 and 0 within apage (reduction of interference between cells or between pages, andequalization). In this manner, the number of times of write can beleveled, and the life of the NAND memory 11 can be increased. Therefore,the reliability of the NAND memory 11 can be enhanced.

The NAND controller (NANDC) 50 accesses the NAND memory 11 in parallelby using a plurality of channels (in this example, four channels CH0 toCH3), in order to meet a predetermined speed requirement.

The CPU 43B controls the above-described respective structuralcomponents (45 to 50, RZ) of the back end 12B, and controls the entireoperations of the back end 12B.

It should be noted that the configuration of the controller 12illustrated in FIG. 22 is merely an example, and is not limited to theillustrated configuration.

[Storage System 100]

FIG. 23 is a perspective view illustrating a storage system 100according the third embodiment.

The storage system 100 includes a plurality of memory systems 10 asSSDs.

The external appearance of the memory system 10 is, for example, arelatively small module, and the outer-shape dimensions are, forinstance, about 120 mm×130 mm. It should be noted that the size anddimensions of the memory system 10 are not limited to these, and properchanges to various sizes are possible.

In addition, the memory system 10 can be used by being mounted in thehost 20 that is an information processing apparatus such as a server, ina data center or a cloud computing system which is operated in a company(enterprise). Thus, the memory system 10 may be an Enterprise SSD(eSSD).

The host 20 includes a plurality of connectors (for example, slots) 30which open upward, for example. Each connector 30 is, for instance, aSAS (Serial Attached SCSI) connector. According to this SAS connector,the host 20 and each memory system 10 can execute high speedcommunication by 6 Gbps dual ports. It should be noted that eachconnector 30 is not limited to this, and may be, for instance, a PCIExpress (PCIe).

The plural memory systems 10 are attached to the connectors 30 of thehost 20, respectively, and are juxtaposed and supported in uprightattitudes in a substantially vertical direction. According to thisconfiguration, the plural memory systems 10 can be mounted in a compactsize, and the size of the memory system 10 can be reduced. Furthermore,the shape of each memory system 10 of the third embodiment is a 2.5 typeSFF (Small Form Factor). By this shape, the memory system 10 can have acompatible shape with an Enterprise HDD (eHDD), and system compatibilitywith the eHDD can be realized.

The memory system 10 is not limited to the use for enterprises. Forexample, the memory system 10 is applicable as a storage medium of aconsumer electronic device such as a notebook computer or a tabletcomputer.

As has been described above, according to the information processingsystem 1 and storage system 100 relating to the third embodiment, thesame advantageous effects as in the above-described first and secondembodiments and Modification 1 can be obtained in connection with largestorage.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A memory system comprising: a nonvolatile memory;and a controller configured to control the nonvolatile memory, whereinthe controller includes: an access controller configured to controlaccess to the nonvolatile memory, based on a first request which isissued from an outside; a processor configured to execute garbagecollection for securing, on the nonvolatile memory, a free area forwriting data in the nonvolatile memory, based on a second request whichis issued from the outside before the first request is issued; and ascheduler configured to schedule the garbage collection by controllingthe processor.
 2. The memory system of claim 1, wherein the firstrequest is a first command which requests write to the nonvolatilememory, and the second request is a second command including a size ofwrite data of the first command.
 3. The memory system of claim 2,wherein the scheduler is configured to control the processor in a mannerto execute the garbage collection until the free area corresponding tothe size of the write data in the second command is generated in thenonvolatile memory.
 4. The memory system of claim 3, wherein the accesscontroller is configured to write the write data in the generated freearea in the nonvolatile memory, based on the first command.
 5. Thememory system of claim 1, wherein the first request is a first commandwhich requests write to the nonvolatile memory, and the second requestis a second command including a size of write data of the first command,and a write start time or hint information capable of specifying a writestart time.
 6. The memory system of claim 5, wherein the scheduler isconfigured to: schedule next garbage collection such that garbagecollection corresponding to the size of the write data is completed ator before the write start time described in the second command; andschedule a start of the garbage collection such that the garbagecollection is executed until the free area corresponding to the size ofthe write data is generated on the nonvolatile memory, and the accesscontroller is configured to write the write data in the free area in thenonvolatile memory, based on the first command.
 7. The memory system ofclaim 1, wherein the first request is a first command which requestswrite to the nonvolatile memory, and the second request is a secondcommand including a size of write data of the first command, and flaginformation instructing execution or stopping of the garbage collection.8. The memory system of claim 7, wherein the outside is configured toissue a third command for inquiring, before the first command is issued,about a size of the free area in the nonvolatile memory generated by thegarbage collection, and to monitor a generation status of the free area.9. The memory system of claim 8, wherein the processor is configured tonotify the outside of the size of the free area in the nonvolatilememory generated by the garbage collection, and to issue a response tothe third command.
 10. The memory system of claim 9, wherein the outsideis configured to issue the first command based on the size of the freearea in the nonvolatile memory described in the response to the thirdcommand, and the processor is configured to write the write data in thefree area in the nonvolatile memory based on the issued first command.11. The memory system of claim 1, wherein the scheduler or the processoris configured to notify the outside of an extended response to thesecond request.
 12. An information processing system comprising: amemory system including a nonvolatile memory; and a host configured todrive the memory system and to request a predetermined operation,wherein the memory system includes: an access controller configured tocontrol access to the nonvolatile memory based on a first request whichis issued from the host; and a processor configured to execute abackground process for the nonvolatile memory based on a second requestwhich is issued from the host before the first request is issued. 13.The information processing system of claim 12, wherein the memory systemfurther includes a scheduler configured to schedule the backgroundprocess by controlling the processor.
 14. The information processingsystem of claim 12, wherein the first request is a first command whichrequests write to the nonvolatile memory, and the second request is asecond command including a size of write data of the first command. 15.The information processing system of claim 14, wherein the backgroundprocess is garbage collection for securing, on the nonvolatile memory, afree area for writing data in the nonvolatile memory, and the scheduleris configured to control the processor in a manner to execute thegarbage collection until a size of the free area in the second commandis generated in the nonvolatile memory.
 16. The information processingsystem of claim 15, wherein the access controller is configured to writethe write data into the generated free area in the nonvolatile memorybased on the first command.
 17. The information processing system ofclaim 12, wherein the first request is a first command which requestswrite to the nonvolatile memory, and the second request is a secondcommand including a size of write data of the first command, and a writestart time or hint information capable of specifying a write start time.18. The information processing system of claim 17, wherein the scheduleris configured to: schedule next garbage collection such that garbagecollection corresponding to the size of the write data is completedbefore the write start time described in the second command; andschedule a start of the garbage collection such that the garbagecollection is executed until the free area corresponding to the size ofthe write data is generated on the nonvolatile memory, and the accesscontroller is configured to write the write data in the free area in thenonvolatile memory based on the first command.
 19. The informationprocessing system of claim 12, wherein the background process includesat least one of block erase, patrol read and refresh process.